Overcoat wire grid polarizer having overcoat layer spanning air-filled channels

ABSTRACT

A wire grid polarizer (WGP) can be durable and have high performance. The WGP can comprise an array of wires  13  on a substrate  11 . An overcoat layer  32  can be located at distal ends of the array of wires  13  and can span channels  15  between the wires  13 . A conformal-coat layer  61  can coat sides  13   s  and distal ends  13   d  of the wires  13  between the wires  13  and the overcoat layer  32 . The overcoat layer can comprise aluminum oxide. An antireflection layer  33  can be located over the overcoat layer  32.

CLAIM OF PRIORITY

This is a continuation of U.S. patent application Ser. No. 15/691,315,filed on Aug. 30, 2017, which claims priority to US Provisional PatentApplication No. 62/425,339, filed on Nov. 22, 2017, and is acontinuation-in-part of U.S. patent application Ser. No. 15/631,256,filed on Jun. 23, 2017, which claims priority to U.S. Provisional PatentApplication No. 62/375,675, filed on Aug. 16, 2016, all of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present application is related generally to wire grid polarizers.

BACKGROUND

A wire grid polarizer (WGP) can be used to divide light into twodifferent polarization states. A high percent of one polarization statecan pass through the WGP and a high percent of the other can be absorbedor reflected. The effectiveness or performance of a WGP is based on avery high percent transmission of one polarization (Tp) and minimaltransmission of an opposite polarization (Ts). It can be beneficial tohave high contrast (Tp/Ts). The percent reflection of the oppositepolarization (Rs) can also be an important indicator of polarizerperformance.

Wires of WGPs, especially for polarization of visible or ultravioletlight, can have small, delicate wires with nanometer-sized pitch,wire-width, and wire-height. WGPs are used in systems (e.g. computerprojectors, semiconductor inspection tools, etc.) that require highperformance. Small defects in the WGP, such as corroded wires andcollapsed wires can significantly degrade system performance (e.g.distorted image from a computer projector). Ordinary handling can causethe wires to collapse. Therefore, it can be important to protect thewires from corrosion and mechanical damage.

Oxidation can degrade performance by adversely affecting contrast and/orRs. As an aluminum wire forms a natural oxide over time, the underlying,substantially-pure aluminum is consumed, thus reducing the size of thesubstantially-pure aluminum wire and changing polarizationcharacteristics of the WGP.

SUMMARY

It has been recognized that it would be advantageous to have high wiregrid polarizer (WGP) performance and to protect the wires fromcorrosion, mechanical damage, and oxidation. The present invention isdirected to various embodiments of a WGP, and methods of making a WGP,that satisfy these needs. Each embodiment or method may satisfy one,some, or all of these needs.

The WGP can comprise an array of wires located over a face of atransparent substrate with channels between adjacent wires. An overcoatlayer can be located at distal ends of the array of wires and can spanthe channels.

In one embodiment, a moisture-barrier layer can coat sides and distalends of the wires between the wires and the overcoat layer. In anotherembodiment, an antireflection layer can be located over the overcoatlayer.

The method of manufacturing a WGP can comprise the following steps inthe following order:

-   1. Providing an array of wires over a face of a transparent    substrate with channels between adjacent wires. The channels can be    air-filled. Each wire can have a cross-sectional profile with a base    located closest to the substrate and a distal end located farthest    from the substrate. Each wire can have opposite sides facing the    channels on opposite sides of the wire, respectively, and extending    from the base to the distal end.-   2. Applying a moisture-barrier layer to the sides and to the distal    ends of the wires while maintaining the channels air-filled.-   3. Applying an overcoat layer, over the moisture-barrier layer, at    the distal ends of the array of wires and spanning the channels, and    maintaining the channels air-filled.

BRIEF DESCRIPTION OF THE DRAWINGS (DRAWINGS MIGHT NOT BE DRAWN TO SCALE)

FIG. 1 is a schematic, cross-sectional side-view of a wire gridpolarizer (WGP) 10 with an array of wires 13 over a face 11 _(f) of atransparent substrate 11, with channels 15 between adjacent wires 13, inaccordance with an embodiment of the present invention.

FIG. 2 is a schematic perspective-view of the WGP 10 of FIG. 1, inaccordance with an embodiment of the present invention.

FIGS. 3-4 are schematic, cross-sectional side-views of WGPs 30 and 40,similar to WGP 10 of FIGS. 1-2, but further comprising an overcoat layer32 at distal ends 13 _(d) of the array of wires 13, the overcoat layer32 spanning the channels 15, and an antireflection layer 33 located overthe overcoat layer 32, in accordance with an embodiment of the presentinvention.

FIG. 5 is a schematic, cross-sectional side-view of a WGP 50, similar toWGP 10 of FIGS. 1-2, but further comprising an overcoat layer 32 atdistal ends 13 _(d) of the array of wires 13, the overcoat layer 32spanning the channels 15 and extending down sides 13 _(s) of the wires13 from a distal end 13 _(d) to a base 13 _(b), in accordance with anembodiment of the present invention.

FIG. 6 is a magnified, schematic, cross-sectional side-view of a portionof a WGP 60 (showing one wire 13), similar to WGP 10 of FIGS. 1-2, butfurther comprising an overcoat layer 32 at a distal end 13 _(d) of thewire 13 and a conformal-coat layer 61 that coats the sides 13 _(s) ofthe wire 13 and the distal end 13 _(d) of the wire 13 between the wire13 and the overcoat layer 32, in accordance with an embodiment of thepresent invention.

FIGS. 7-8 are schematic views of image projectors 70 and 80, each withat least one WGP 74, in accordance with embodiments of the presentinvention.

DEFINITIONS

As used herein, the term “conformal-coat layer” means a layer thatconforms to a topology of the WGP.

As used herein, the term “degradation of Rs” means an increase in Rs fora selectively-absorptive WGP or a decrease in Rs for a reflective WGP.

As used herein, the term “elongated” means that a length L of the wires13 is substantially greater than wire width W or wire thickness Th₁₃(see FIGS. 1-2). For example, WGPs for ultraviolet or visible light canhave a wire width W between 20 and 100 nanometers and wire thicknessTh₁₃ between 50 and 500 nanometers; and wire length L of about 1millimeter to 20 centimeters or more, depending on the application.Thus, elongated wires 13 can have a length L that is many times (e.g. atleast 10 times, at least 100 times, at least 1000 times, or at least10,000 times) larger than wire width W and/or wire thickness Th₁₃. Theterm “elongated” can also mean that the length L of the wires 13 islonger than any wavelength in the wavelength range of intended use. Forexample, the length L can be greater than 700 nm, the longest wavelengthof visible light.

As used herein, the term “located on” means located directly on orlocated above with some other solid material between.

As used herein, the term “Tp” means a percent transmission of apredominantly-transmitted polarization (usually p-polarization); theterm “Ts” means a percent transmission of the opposite polarization(usually s-polarization); and the term “Rs” means a percent reflectionof the opposite polarization.

DETAILED DESCRIPTION

As illustrated in FIGS. 1-2, a wire grid polarizer (WGP) 10 is showncomprising an array of wires 13 located over a face 11 _(f) of atransparent substrate 11. The array of wires 13 can besubstantially-parallel and elongated, with channels 15 between adjacentwires 13. The channels 15 can be filled with a solid, a liquid, avacuum, or a gas, such as air. Each wire 13 can have a cross-sectionalprofile with a base 13 _(b) located closest to the substrate 11, adistal end 13 _(d) located farthest from the substrate 11, and oppositesides 13 _(s) facing the channels 15 on opposite sides 13 _(s) of thewire, respectively, and extending from the base 13 _(b) to the distalend 13 _(d). Each wire 13 can be made of or include materials forpolarization of light, including metals and/or dielectrics, as aretypically used in wires of wire grid polarizers. See for example U.S.Pat. Nos. 7,961,393 and 8,755,113, which are incorporated herein byreference.

As shown in FIGS. 3-6, an overcoat layer 32 can be located at the distalends 13 _(d) of the array of wires 13 and can span the channels 15. Theovercoat layer 32 can provide structural-support for the wires 13 tokeep them from toppling, and may allow handling and cleaning the WGP 30,40, or 50.

The overcoat layer 32 can span the channels 15 with minimal overcoatlayer 32 entering the channels 15 as shown in FIGS. 3-4 and 6.Alternatively, the overcoat layer 32 can extend most or all of the waydown the sides 13 _(s) of the wires 13 as shown in FIG. 5.

The overcoat layer 32 can be a transparent dielectric, such as silicondioxide for example. Careful selection of a material of the overcoatlayer 32 can help avoid performance degradation of the WGP over time.For example, the overcoat layer 32 can comprise aluminum oxide which canprotect the wires 13 from oxidation. A material composition of theovercoat layer 32 can be at least 99 mass percent aluminum oxide in oneaspect, at least 90 mass percent aluminum oxide in another aspect, atleast 50 mass percent aluminum oxide in another aspect, or at least 20mass percent aluminum oxide in another aspect.

Due to imperfections in deposition of the overcoat layer 32, material ofthe overcoat layer 32 might not be in exact stoichiometric ratios. Forexample, the term aluminum oxide (Al₂O₃) means approximately twoaluminum atoms for every three oxygen atoms, such as for exampleAl_(x)O_(y), where 1.9≤x≤2.1 and 2.9≤y≤3.1.

Causing the overcoat layer 32 to extend part or all of the way down thesides 13 _(s) from the distal end 13 _(d) to the base 13 _(b), as shownin FIG. 5, can protect the sides 13 _(s) of the wires 13 from oxidation.The overcoat layer 32 can include a thickness Th₃₂ along the sides 13_(s) of between 10 and 100 nanometers. The overcoat layer 32 can havethis thickness Th₃₂ at certain location(s) along the sides 13 _(s) oralong both sides 13 _(s) from the distal end 13 _(d) to the base 13_(b). Even with the overcoat layer 32 extending down the sides 13 _(s)of the wires 13, the channels 15 can still be air-filled. Alternatively,because the overcoat layer 32 can adversely affect performance due toits index of refraction, it can extend only part-way down the sides 13_(s) of the wires from the distal end 13 _(d) to the base 13 _(b), suchas for example <25% of the way in one aspect or between 10% and 50% ofthe way in another aspect.

WGPs described herein can have one or more of the followingdifferentials between performance measured prior to a durability testand after the durability test: <0.01% increase of Ts, <0.005% increaseof Ts, <0.001% increase of Ts, <1% degradation of Rs, <0.5% degradationof Rs, and <0.25% degradation of Rs. These values can be for a singleWGP or can be averaged across 100 WGPs. The durability test is performedat a temperature of 300° C. for 168 hours or 500 hours. The durabilitytest is performed immediately after manufacturing, or within three weeksafter manufacturing if the WGP is maintained in a protected environment(e.g. room temperature, protected from ultraviolet light, low humidity,etc.), Without the overcoat layer 32, there was an average of about0.04% increase of Ts and an average of about 3% degradation of Rs afterthe same durability test for 168 hours.

Prior to this invention, a primary failure of WGPs was toppled wires 13.Because the wires 13 were tall (e.g. about 200-400 nm) but not very wideW (e.g. about 50-70 nm), and the distal ends 13 _(d) of the wires 13were not secured, the wires 13 easily toppled. The inventors desired tocreate a stronger WGP with wires 13 that were less susceptible totoppling. Related US patent publications include US 2003/0224116, US2012/0075699, U.S. Pat. Nos. 6,288,840, 6,665,119, and 7,026,046, whichinclude some ideas for improving durability that have not been widelyused, even though durability has been a very important issue, becausesome of these can also cause a substantial drop in WGP performance.

The inventors anticipated a significant drop in performance caused byaddition of the overcoat layer 32, but added the overcoat layer 32anyway because of a need for increased wire stability. The inventorsdiscovered that performance drop, caused by addition of the overcoatlayer 32, could be avoided by adding an antireflection layer 33 locatedover the overcoat layer 32 (see FIGS. 3-4). The overcoat layer 32 canprovide a base or foundation for applying the antireflection layer 33.Any performance drop, caused by addition of the overcoat layer 32, canbe avoided or minimized by adding the antireflection layer 33 over theovercoat layer 32. Quantification of this performance is described belowin the METHOD section.

As shown on WGP 30 in FIG. 3, the antireflection layer 33 can includemultiple thin-film layers 31 located on the overcoat layer 32, extendingcontinuously across the overcoat layer 32, and capable of reducingreflection of incident light on the overcoat layer 32. One example of athin-film antireflection layer 33 is: at least two pairs of layers witheach pair including a layer of silicon dioxide and a layer of 95% ZrO₂plus 5% TiO₂, and a thickness of each layer is between 30 and 300nanometers.

As shown on WGP 40 in FIG. 4, the antireflection layer 33 can includemultiple protrusions 41, formed in an array, located on the overcoatlayer 32. The protrusions 41 can be designed for reducing reflection ofincident light on the overcoat layer 32. For example, each protrusion 41can have a width W₄₁ and a height H₄₁ that are less than 700 nanometers.

As shown in FIG. 6, a conformal-coat layer 61 can be located over thewires 13. The conformal-coat layer 61 can cover an exposed surface ofthe wires 13. The conformal-coat layer 61 can also be located over anexposed surface of the substrate 11 (“exposed surface” meaning a surfaceof the substrate not covered with wires 13). Use of a conformal-coatlayer 61 can be beneficial because by following a contour of the wires13 and an exposed surface of the substrate 11, conformal-coat layer 61thickness T₆₁ can be minimized, thus reducing any detrimental effect ofthe conformal-coat layer 61 on WGP performance. For example, a maximumthickness of the conformal-coat layer 61 can be <5 nanometers (nm) inone aspect, <10 nm in another aspect, <25 nm in another aspect, or <50nm in another aspect.

The conformal-coat layer 61 can include an oxidation-barrier layer, amoisture-barrier layer, or both. Oxidation of WGP wires 13 can degradeperformance of the WGP, by adversely affecting contrast or Rs. Anoxidation-barrier layer can reduce oxidation of the wires 13, and thusreduce or avoid such WGP performance degradation. The term“oxidation-barrier” means a first material capable of reducing theingress of oxygen into a second material, which may cause the secondmaterial to oxidize. An oxidation barrier can be placed on the wires 13to protect the wires 13 from oxidation. Non-limiting examples ofchemicals that can be used as an oxidation-barrier layer include:aluminum oxide, silicon oxide, silicon nitride, silicon oxynitride,silicon carbide, or combinations thereof.

WGP corrosion can degrade WGP performance. For example, water cancondense onto the WGP and wick into narrow channels 15 between wires 13due to capillary action. The water can then corrode the wires 13.Corroded regions can have reduced contrast, changed Rs, or can fail topolarize at all. A moisture-barrier layer can resist corrosion. Amoisture-barrier layer can protect the wires 13 from water or othercorrosion. Examples of chemicals that can be used as a moisture-barrierlayer include, but are not limited to: hafnium oxide, zirconium oxide,amino phosphonate, or combinations thereof. Examples of corrosionprotection chemistry are described in US patent publications U.S. Pat.No. 6,785,050 and US 2016/0291209, which are both incorporated herein byreference in their entirety.

The conformal-coat layer 61 can include rare earth oxides, for example,oxides of scandium, yttrium, lanthanum, cerium, praseodymium, neodymium,promethium, samarium, europium, gadolinium, terbium, dysprosium,holmium, erbium, thulium, ytterbium, and lutetium. These rare earthoxides can be at least part of the oxidation-barrier layer, themoisture-barrier layer, or both.

The conformal-coat layer 61 can be distinct from the wires 13, meaning(1) there can be a boundary line or layer between the wires 13 and theconformal-coat layer 61; or (2) there can be some difference of materialof the conformal-coat layer 61 relative to a material of the wires 13.For example, a native aluminum oxide can form at a surface of aluminumwires 13. A layer of aluminum oxide (oxidation-barrier layer) can thenbe applied to the ribs (e.g. by ALD). This added layer of aluminum oxidecan be important, because a thickness and/or density of the nativealuminum oxide can be insufficient for protecting a core of the wires 13(e.g. substantially pure aluminum) from oxidizing. In this example,although the oxidation-barrier layer (Al₂O₃) has the same materialcomposition as a surface (Al₂O₃) of the wires 13, the oxidation-barrierlayer can still be distinct due to (1) a boundary layer between theoxidation-barrier layer and the wires 13 and/or (2) a difference inmaterial properties, such as an increased density of theoxidation-barrier layer relative to the native aluminum oxide.

Image Projector

The WGPs described herein can be used in an image projector, such as forexample image projector 70 shown in FIG. 7 or image projector 80 shownin FIG. 8. The image projector 70 or 80 can comprise a light source 71or 81 capable of emitting a beam of light 73 or 83, spatial lightmodulator(s) 77, and WGP(s) 74 according to WGP embodiments describedherein.

The spatial light modulator 77 can be located to receive at least partof the beam of light 73 or 83. The spatial light modulator 77 can have aplurality of pixels, each pixel capable of receiving a signal. Thesignal can be an electronic signal. Depending on whether or not eachpixel receives the signal, or the strength of the signal, the pixel canrotate a polarization of, or transmit or reflect without causing achange in polarization of, a part of the beam of light 73 or 83. Thespatial light modulator(s) 77 can be a liquid crystal device/display(LCD) and can be transmissive, reflective, or transflective.

The WGP(s) 74 can be located in at least part of the beam of light 73 or83 prior to entering the spatial light modulator 77, after exiting thespatial light modulator 77, or both. The WGP(s) 74 help form the imageby providing polarized light to the spatial light modulator 77 and bytransmitting, reflecting, or absorbing light from each pixel of thespatial light modulator 77 depending on the type and rotation of WGP 74and whether each pixel received the signal.

A projection lens system 75 can be located to receive at least part ofthe beam of light 73 or 83 and can project an image. Projection lenssystems 75 are described in U.S. Pat. Nos. 6,585,378 and 6,447,120,which are hereby incorporated herein by reference in their entirety.Alternatively, the beam of light 73 or 83 can be emitted directly intoan eye of a user or into another device instead of into the projectionlens system 75.

As shown in FIG. 7, the image projector 70 can further comprisecolor-splitting optics 72 and color-combining optics 78. The lightsource 71 can emit a beam of light 73, which can initially beunpolarized. The color-splitting optics 72 can be located to receive atleast part of the beam of light 73, can be located between the lightsource 71 and the spatial light modulator 77 and can split the beam oflight 73 into multiple, differently-colored light beams, definingcolored beams 73 _(c). The colored beams 73 _(c) can be primary colors.

The color-combining optics 78 can be located between the spatial lightmodulator 77 and the projection lens system 75 (or the eye of the useror other device) and can be located to receive at least part of thecolored beams 73 _(c). The color-combining optics 78 can recombine atleast part of the colored beams 73 _(c) into a final beam or combinedbeam 73 _(f). Color-combining optics 78 are used in computer projectorsfor combining different colors of light into a single image to beprojected. Color-combining optics 78 are sometimes called X-Cubes,X-Cube prisms, X-prisms, light recombination prisms, or cross dichroicprisms. X-Cubes are typically made of four right angle prisms, withdichroic coatings, that are cemented together to form a cube.

The projection lens system 75 can be located to receive the combinedbeam 73 _(f) and can project a colored image 73 _(i). The colored image73 _(i) can be projected onto a screen 76 or into an eye of a person.

The spatial light modulator 77 can be located to receive, in a lightpath between the color-splitting optics 72 and the color-combiningoptics 78, at least one of the colored beams 73 _(c). The imageprojector 70 can include a spatial light modulator 77 for each of thecolored beams 73 _(c). The WGP(s) 74 can be located in at least one ofthe colored beams 73 _(c) prior to entering the spatial light modulator77, after exiting the spatial light modulator 77, or both.

As shown on image projector 80 in FIG. 8, the light source 81 cansequentially emit multiple, differently-colored light beams, definingcolored beams 83. The colored beams 83 can be primary colors. Theprojection lens system 75 (or the eye of the user or other device) canbe located to receive the colored beams 83 and can project a coloredimage 73 _(i). The colored image 73 _(i) can be projected onto a screen76 or into an eye of a person. The spatial light modulator 77 can belocated to receive, in a light path between the light source 81 and theprojection lens system 75, the colored beams 83. The WGP 74 can belocated in the colored beams 83 prior to entering the spatial lightmodulator 77, after exiting the spatial light modulator 77, or both.

Method

A method of manufacturing a WGP can comprise some or all of thefollowing steps, which can be performed in the following order. Theremay be additional steps not described below. These additional steps maybe before, between, or after those described.

-   1. Providing an array of wires 13 located over a face 11 _(f) of a    transparent substrate 11. The array of wires 13 can be    substantially-parallel and elongated, with channels 15 between    adjacent wires 13. The channels 15 can be air-filled. Each wire 13    can have a cross-sectional profile with a base 13 _(b) located    closest to the substrate 11 and a distal end 13 _(d) located    farthest from the substrate 11. Each wire 13 can have opposite sides    13 _(s) facing the channels 15 on opposite sides 13 _(s) of the    wire, respectively, and extending from the base 13 _(b) to the    distal end 13 _(d). See FIGS. 1-2.-   2. Applying a conformal-coat layer 61 to the sides 13 _(s) and to    the distal ends 13 _(d) of the wires 13 while maintaining the    channels 15 air-filled. Methods of applying the conformal-coat layer    61 include sputter deposition and evaporation. Applying the    conformal-coat layer 61 can include one of the following: (i)    applying an oxidation-barrier layer then a moisture-barrier    layer; (ii) applying the moisture-barrier layer then the    oxidation-barrier layer; or (iii) applying the moisture-barrier    layer or the oxidation-barrier layer. See FIG. 6 and description of    the oxidation-barrier layer, moisture-barrier layer, and    conformal-coat layer 61 above.-   3. Applying an overcoat layer 32, over the conformal-coat layer 61,    at the distal ends 13 _(d) of the array of wires 13, and spanning    the channels 15 and maintaining the channels 15 air-filled. The    overcoat layer 32 can include materials as described above, with    mass percent as described above. The overcoat layer 32 can extend    down the sides 13 _(s) of the wires 13 from the distal end 13 _(d)    to the base 13 _(b). The overcoat layer 32 can include various    thicknesses T₃₂ along the sides 13 _(s) of the wires 13, such as for    example between 10 and 100 nanometers. The overcoat layer 32 can be    applied by sputter deposition. See FIGS. 3-5 and description of the    overcoat layer 32 above.-   4. Applying an antireflection layer 33 over the overcoat layer 32.    See FIGS. 3-4 and description of the antireflection layer 33 above.

In the above method, some or all of the performance lost by applying theovercoat layer 32 can be regained by applying an antireflection layer33. Thus, one or more of the following equations can be true:Tp₁−Tp₂<2%, Tp₁−Tp₂<1.5%, Tp₁−Tp₂<1%, or Tp₁-Tp₂<0.5%, where thesubscript 1 refers to performance before applying the overcoat layer 32and subscript 2 refers to performance after applying the antireflectionlayer 33.

What is claimed is:
 1. A wire grid polarizer (WGP) comprising: an arrayof wires located over a face of a transparent substrate, the array ofwires being substantially-parallel and elongated, with channels betweenadjacent wires; each wire of the array of wires having: across-sectional profile with a base located closest to the substrate anda distal end located farthest from the substrate; and opposite sidesfacing the channels on opposite sides of the wire, respectively, andextending from the base to the distal end; an overcoat layer, comprisingaluminum oxide, located at the distal ends of the array of wires andspanning the channels, the channels being air-filled; a conformal-coatlayer which is distinct from the wires and that coats the sides of thewires, the distal ends of the wires between the wires and the overcoatlayer, and an exposed surface of the substrate; and the entireconformal-coat layer has a maximum thickness of <25 nm.
 2. The WGP ofclaim 1, wherein the maximum thickness is <5 nm.
 3. The WGP of claim 1,wherein the maximum thickness is <10 nm.
 4. The WGP of claim 1, whereinthe overcoat layer comprises at least 90 mass percent aluminum oxide. 5.The WGP of claim 1, wherein the conformal-coat layer at a distal end ofeach wire does not touch the conformal-coat layer at the distal end ofadjacent wires, the distal end being a farthest end of the wires fromthe substrate.
 6. The WGP of claim 1, wherein the conformal-coat layerincludes amino phosphonate.
 7. A wire grid polarizer (WGP) comprising:an array of wires located over a face of a transparent substrate, thearray of wires being substantially-parallel and elongated, with channelsbetween adjacent wires; each wire of the array of wires having: across-sectional profile with a base located closest to the substrate anda distal end located farthest from the substrate; and opposite sidesfacing the channels on opposite sides of the wire, respectively, andextending from the base to the distal end; an overcoat layer located atthe distal ends of the array of wires and spanning the channels, thechannels being air-filled; and a conformal-coat layer that entirelyconforms to a topology of the wires and coats the sides of the wires,the distal ends of the wires between the wires and the overcoat layer,and an exposed surface of the substrate.
 8. The WGP of claim 7, whereinthe overcoat layer comprises aluminum oxide.
 9. The WGP of claim 7,further comprising an antireflection layer over the overcoat layer, theantireflection layer including multiple protrusions formed in an array,the protrusions designed for reducing reflection of incident light onthe overcoat layer, and each protrusion having a width and a height ofless than 700 nanometers.
 10. The WGP of claim 7, further comprising anantireflection layer located over the overcoat layer, the antireflectionlayer including multiple thin-film layers extending continuously acrossthe overcoat layer and capable of reducing reflection of incident lighton the overcoat layer, the multiple thin-film layers including at leasttwo pairs of layers, each layer with a thickness of between 30 and 300nanometers.
 11. The WGP of claim 7, wherein the conformal-coat layerincludes hafnium oxide.
 12. The WGP of claim 7, wherein theconformal-coat layer includes zirconium oxide.
 13. The WGP of claim 7,wherein the conformal-coat layer includes a rare earth oxide.
 14. TheWGP of claim 7, wherein the conformal-coat layer is distinct from thewires, and the conformal-coat layer includes aluminum oxide, siliconoxide, silicon nitride, silicon oxynitride, silicon carbide, orcombinations thereof.
 15. The WGP of claim 14, wherein theconformal-coat layer includes amino phosphonate.
 16. The WGP of claim 7,wherein a maximum thickness of the entire conformal-coat layer is <10nm.
 17. The WGP of claim 7, wherein a maximum thickness of the entireconformal-coat layer is <25 nm.
 18. The WGP of claim 7, wherein theconformal-coat layer at a distal end of each wire does not touch theconformal-coat layer at the distal end of adjacent wires, the distal endbeing a farthest end of the wires from the substrate.
 19. The WGP ofclaim 7, wherein the conformal-coat layer includes amino phosphonate.20. The WGP of claim 7, wherein the conformal-coat layer includesaluminum oxide and hafnium oxide and the entire conformal-coat layer hasa maximum thickness of <25 nm.